This section provides background information related to the present disclosure which is not necessarily a prior art.
FIG. 1 is a schematic view showing an example of a system and method for generating Positron Emission Tomography (PET)-Computed Tomography (CT) images disclosed in U.S. Pat. No. 7,447,345. FIG. 1 shows a PET-CT scanner 100. The PET-CT scanner 100 includes a CT system 200 and a PET system 300. The CT system 200 and the PET system 300 are mounted on a housing 120. Furthermore, the PET-CT scanner 100 includes a patient table 113, a bed 114, a processing unit 150, and a control station 115. The bed 114 is movable to the housing 120 by a manipulation of the control station 115. In general, the control station 115 includes a monitor and a keyboard. The processing unit 150 processes medical images obtained by the CT system 200 and the PET system 300 in response to a manipulation of the control station 115.
A Positron Emission Computed Tomography (PET) test is an advanced nuclear medicine image test method for dosing positron emission radioactive isotopes, obtaining radiation emitted outside the body, and obtaining useful diagnostic information related to a metabolic change of the body. Recently, this technology takes a step forward from obtaining only simple PET images and gradually evolves into a hybrid scanner into which even Computed Tomography (CT) equipment or Magnetic Resonance Image (MRI) equipment has been fused. In the current PET test, a PET/CT scanner in which a PET system and a CT system are coupled to the same body is used, and anatomical information from a CT image is obtained, so that the precise position and depth information of a lesion checked in a PET image can be provided.
Such a fusion or alignment (or registration) of images is possible when a sequentially obtained CT image and PET image are completely matched up with each other basically on the same plane, that is, when the two images are accurately matched (i.e., accurate registration). If a mismatch (i.e., mismatch registration) occurs between the two images due to a problem in a test, there is a limit in providing position information, that is, the original object of the fusion or alignment.
In particular, in a PET image, partial images at the positions of the bed 114 corresponding to a length of about 20 cm or less may be obtained due to a limit of an axial field of view (aFOV) inside and outside the length and a total body image may be configured by combining the partial images. In general, it is a precondition that a movement of a patient be minimized during a test in obtaining a medical image obtained by combining images at several bed positions. For example, such a problem may not be easily solved because the time taken to obtain a PET image, for example, is currently about 15 minutes. Furthermore, when a test is performed from the head to the feet, problems, such as the generation of an image artifact and a loss of a lesion near the pelvis area, are generated due to radioactivity of remaining urine filled in a bladder. For this reason, a test is performed from the feet to the head. If a test is performed from the feet to the head, however, an image mismatch near the head and a neck part attributable to a movement of the head during the test is frequently monitored while the head is photographed. FIGS. 2 and 3 are photographs showing an example in which a mismatch has occurred in a fusion image of a PET image and a CT image due to a movement of the head of a patient who experiences a total body PET test during the test. FIG. 2 is a transverse photograph in which a mismatch has occurred in the head, and FIG. 3 is a transverse photograph in which a mismatch has occurred a nose portion. FIG. 4 is a photograph showing a mismatch between a PET image and a CT image attributable to a movement of an arm during a test and an image artifact corresponding to the mismatch.